1. Field of the Invention
The present invention concerns a novel azo compound and, in particular, it relates to a novel azo dye and a tautomeric isomer thereof having favorable hue and light fastness.
2. Description of the Related Art
Since azo compounds have absorption of various visible lights, they have conventionally been used in various fields as dyes. Azo compounds have been used, for example, for coloration of synthetic resins, printing inks, sublime thermal transfer material dyes and ink jet recording inks and have also been used recently in the field of electronics as functional dyes.
One of the important properties required of azo compounds as dyes is the absorption spectrum. The hue of a dye gives an effect on the color and aesthetic property of an article to be colored by the dye and has a significant visual effect. Accordingly, studies on the absorption spectra of dyes have long been widely studied and are described in literature such as “Light Absorption of Organic Colorants” by J. Fabian and H. Hartmann (Springer-Verlag, Berlin, 1980).
Further, performances required of dyes have become varied depending on the application use. It has been required for dyes to have a plurality of functions depending on the application uses in many cases, such that, for example, a dye of brilliant hue and favorable dyeability is desired when dying sheep skins or cow skins, and a dye of less water solubility and of brilliant hue is desired to allow laundry in the case of clothing ornaments. In addition, in the case of use, particularly, for printing inks, sublime thermal transfer material dyes and ink jet recording inks, it has been strongly demanded that durability against light (light fastness) under various environmental conditions is high, in addition to brilliant hue.
In order to solve the improvement of the light fastness of a dye, various diazo compounds or couplers are disclosed (for example in Japanese Patent Application Laid open (JP-A) No. 4-59287 and JP-A No. 4-201483. While the light fastness is improved to some extent thereby, it is not yet sufficient and there remains room for further improvement of light fastness.
Further, as an attempt to improve the light fastness, azo dyes containing quaternary salts have been proposed (for example, in JP-A No. 2002-129047 and the specification of DE No. 19805554). However, these still provide only slight improvements and satisfactory light fastness performance has not yet been attained.
As described above, it is important for dyes to be capable of maintaining brilliance and density even when they are exposed to light or the like for a long time, and at present no azo dye compounds having favorable light resistant performance have yet been provided by the existing techniques described above.